Transport network infrastructure, such as rail network infrastructure, will typically comprise some structures that it is desirable to monitor the condition of. For instance it may be desired to monitor the condition of tunnels that form part of the network to detect any faults in the tunnel that could lead to failure.
In some rail networks the condition of tunnels may be manually inspected. This may comprise an inspection by suitable personnel, including a visual inspection and/or performance of various tests or measurements to identify any potential problems. For instance, the condition of the walls may be visually inspected, the relative position of known markers measured for any movement and in some instances the wall condition may be tested using suitable probes.
Clearly however such inspections require sending an inspection team to the relevant structure and the inspection can take significant time. The area to be inspected, even in a single track rail tunnel of a few hundred meters in length, may be significant and some tunnels may large enough to house multiple tracks and be of the orders of kilometers in length. The inspection may only be possible in times when the relevant section of rail network is not in use, which may limit the time available for inspection and/or result in reduced or cancelled services on the network. For these reasons manual inspection is typically a time consuming and costly undertaking and most infrastructure is therefore inspected only periodically, in some instances with significant periods of time between inspections.
In some structures there may also be a number of permanently installed sensors to provide on-going structural health monitoring. For instance various strain sensors, accelerometers etc. and the like may be deployed through a tunnel to detect any motion. Such sensors are typically point sensors and thus providing adequate coverage for a tunnel, which may be kilometers in length, requires many such sensors with consequent expense. For remote monitoring each sensor must have a suitable power supply and be arranged to be able to transmit the acquired data for analysis.